/Engine/Source/Runtime/SlateCore/Public/Rendering/SlateRenderer.h
Prepares the renderer to take a screenshot of the UI. The Rect is portion of the rendered output that will be stored into theTArrayof FColors.
virtual void PrepareToTakeScreenshot ( const FIntRect & Rect, [TArray](API\Runtime\Core\Containers\TArray)< [FColor](API\Runtime\Core\Math\FColor) > * OutColorData, [SWindow](API\Runtime\SlateCore\Widgets\SWindow) * InScreenshotWindow )